Exhaust muffler for pneumatic tool



y 3953 w. J. BAKEVR ET AL I 3,384,200

EXHAUST MUFFLER FOR PNEUMATIC TOOL Filed March 16, 1967 WILL/AM J BAKERJAMES H. 190E651? INVENTORS ATTORNEY United Stat 3,3342% Patented May21, 1968 3,384,200 EXHAUST MUFFLER FOR PNEUMATIC TOOL William J. Baker,Reed City, and James H. lloeger, Grand Haven, Mich., assignors toGardner-Denver Qompany, a corporation of Delaware Filed Mar. 16, 1967,Ser. No. 623,591 7 Claims. (Cl. 181-36) ABSC'I F THE DECLOSURE A noisemufiling attachment for the exhaust outlet of an air motor-operated toolcomprising a hollow plug having exhaust air flow apertures openingradially from its interior and a tubular sleeve coaxially disposed aboutthe exterior of the plug for collecting and directing the exhaust forfinal discharge through an annular orifice defined between the plug andthe sleeve.

Background of the invention Air tools of the type driven by rotary airmotors usually display undesirable noise characteristics due to thepulsating flow of high pressure air from the motor exhaust toatmosphere. In pistol-grip hand tools, it is common to exhaust motiveair through the handle portion of the tool as shown in US. Patent No.2,966,138 issued to Quackenbush and US. Patent No. 3,299,781 issued toLaw. Both of these prior patents provide noise mufiling means associatedwith the handle exhaust passage. Quackenbush suggests placing mufilingmeans inside the handle passage; and Law shows a muffiing device closingthe exhaust passage and extending beyond the bottom of the handle. U.S.Patent 2,950,775 issued to Zwayer also discloses an external mufllingdevice which is fitted into the bottom of a handle grip for receivingexhaust air from an exhaust passage in the handle. In each of the aboveidentified patents, the noise mufiling action is generally accomplishedby some diffuser means for breaking up the exhaust flow stream into alarge number of randomly directed streams. For this purpose, mufilingelements generally comprise porous metal filters, interwoven screens,bafiles, fibrous packings, porous rubber plugs, and the like. While allof these materials will produce noise muffiing, it is diflicult, if notimpossible, to produce and maintain substantially uniform,predeterminable effects on the exhaust air as the latter flows throughthe muffling material because of changes in the density of compactablematerials and random changes in flow characteristics, such as inducedturbulence, of the exhaust stream as the latter passes throughstructurally deformable screens and bafiles. Such nonuniformity in theflow of high pressure air through conventional mufflers frequentlyproduces undesirable variations in the noise attenuating characteristicof the muffler and in the pressure drop across the mufiler. It is anobject of this invention to eliminate, or at least greatly reduce, suchvariations so that certain preset optimum operational characteristics ofair tool mutlllers can be maintained.

Summary of the invention The invention resides in the combination of anairoperated tool with an exhaust muffler device which is attachable tothe tool casing between the air motor of the tool and atmosphere. Themutlier device is very simply and cheaply made of a hollow plug havingone end detachably threaded into an exhaust outlet passage of the toolhandle and a tubular sleeve disposed about the plug in coaxial relationtherewith. The sleeve and plug are made of metal or other rigid materialof low porosity. The interior cavity of the plug opens near one endthrough a plurality of radially bored, angularly spaced apertures ofpredetermined size, shape and number to produce omnidirectional, lateraldiffusion of the exhaust air stream. The surrounding sleeve is coaxiallyspaced with respect to the plug to define an elongated annularexhaust-receiving chamber between the plug and the sleeves which opensthrough an annular orifice to the exterior of the tool casing. In itsassembled condition, an internal flange of the sleeve is clamped betweenthe plug and the tool casing to close one end of the exhaust-receivingchamber and to insure that the facing Walls of the plug and the sleeveare coaxially spaced along the full length of the orifice therebyproviding a fixed orifice of uniform radial dimension for the finalefilux of exhaust air to atmosphere. Since the sleeve and plug arefabricated of rigid material and the apertures in the plug and theorifice defined between the sleeve and plug are fixed in size and shape,the air flow characteristics of this mufiler device will remain constantwhereby optimum preset noise attenuation and pressure drop through themufller will not vary due to air pressure induced compaction of mulilermaterial or deformation of muffler parts.

These and other objects of the invention will become apparent uponreading the following description and claims in connection with theattached drawings in which:

FIGURE 1 is a side view of an air motor-operated tool having a portionof the casing broken away;

FIG. 2 is an enlarged fragment of the casing handle shown in FIG. 1 withthe mufiler device shown in section;

FIG. 3 is an enlarged bottom view of the handle shown in FIG. 1; and

FIG. 4 is a section taken along lines 44 of FIG. 2.

In the drawings, the numeral 19 generally designates the casing of ahand-held, pistol-grip tool of the air motoractuated type which iscommonly employed as a drill, impact wrench, nut-setter, screw driver,wire wrapper and the like. The output spindle 11 of the tool isrotatively driven by a motor 12 housed in the casing 10 and to whichhigh pressure motive air is supplied by means of a conduit 14% attachedto the casing handle 16 and by an air inlet passage 18 in the handlewhich communicates with the air inlet port of the motor 12. Sliding vanemotors are commonly employed with hand-held tools of the aforedescribedtype and, if such a motor is permitted to exhaust directly toatmosphere, roaring or whining is created due to the pressure variationsor pulsations in the exhaust air. However, in accordance with thisinvention such objectionable noise is reduced or eliminated since themotor exhaust is expelled through an exhaust passage 20 in the handleand then through an exhaust mulller, indicated generally by numeral 22.

The mufller 22 comprises a generally cylindrical plug member 24 and atubular sleeve 26 which telescopingly surrounds a portion of the plug inspaced relation thereto. The plug 24 is provided with a central cavity28 opening upwardly and closed at the bottom by a wall 30 which definesthe lower end of the plug. A major portion of the length of the wall 32of the plug is provided with external threads 34 which engage withmating internal threads 30 formed in the lower portion of the exhaustpassage 20.

A plurality of apertures 38 open through the plug wall 32 to the cavity28 in that portion of the plug wall which extends downwardly beyond thebottom surface 40 of the tool handle 16. As shown in FIG. 4, theapertures open radially through the plug wall and are angularly spacedat even intervals from one another with the longitudinal axes of theapertures lying in a common plane at a right angle to the longitudinalaxis of the cavity 28. A portion of the plug end wall 30 is providedwith an enlarged annular flange 42; and, the apertures 38 open above theflange 42 to the exterior surface 44 of the plug wall 32. As best shownin FIG. 3, a transverse slot 46 is relieved in the bottom surface of theplug end wall 33 for engagement a by a suitable implement for rotatingthe plug 24- to assemble or disassemble the threads 34 and 36.

The aforementioned sleeve 25 includes a radially inwardly extendingannular collar or flange 48 and a depending tubular skirt 50. Theinternal diameter of the collar 48 is sized so that the threaded upperend of the plug 24 may be inserted upwardly thercinto until the bottomsurface 52 of the collar bears upon an annular shoulder 54 whichprojects from the wall 32 of the plug 24 in the manner shown in FIG. 2.When the plug threads 34- are in full engagement with the threads 36 inpassage 20, the collar 48 is rigidly clamped between the plug shoulder54 and the bottom handle surface 4d. Thus, when the plug 24 is properlyattached to the handle 16 by the engagement of the threads 34 and 36, asshown in FIG. 2, the sleeve 26 is clampingly secured in assembledrelation with the plug 24 and the handle 16 so that the skirt 50 iscoaxial with and spaced from the plug. As a result, an annularexhaust-receiving chamber 56 is defined between the wall 44 and theinner skirt wall 58; and, an annular H orifice 6G is defined betweenfacing surfaces of the plug bottom wall 30 and the inner cylindricalwall of the skirt 56. For a purpose to be more fully disclosed, it ispreferable that the aforedescribed clamping of the sleeve collar 48 willrigidly secure the sleeve 26 and plug 24 to the handle 16 to provide theorifice 60 with a cross section of substantially uniform radialdimension.

Preferably, the plug and sleeve which make up the mufiler 22 are simplyand inexpensively fabricated from steel or other metal having highstrength, particularly good resistance to bending or denting due toimpacting. However, certain engineering-grade plastic materials offeringgood dimensional stability and high impact strength are acceptable.

In the operation of the illustrative tool, the motor 12 is energized bydepressing a trigger 62 which opens a suitable valve 63 in the air inletpassage 13 to admit motive air to the motor 12. Exhaust air is expelledfrom the motor 12 through the exhaust passage 20 into the plug cavity28, through the apertures 38 into the chamber 56, and, finally, throughthe annular orifice 60 to atmosphere. The radially directed apertures 33cause the exhaust air to change direction abruptly and to be broken upor diffused into a plurality of streams thereby damping the soundpressure variation in the air flow and changing the flow pattern of theexhaust air to produce noise attenuation. The exhaust air is thencollected or recombined in the exhaust chamber 56; and, with anotherchange in direction of flow, the sound pressure variations are furtherdamped and the air is then emitted through the orificc 60 to theexterior of the casing 10. The skirt 50 may be extended as desiredbeyond the bottom of the plug 26 to directionalize more highly theexhaust flow from the orifice 60 if this should be advantageous incertain tool applications.

The sound attenuating characteristic of the muffler 22 ispredeterminable primarily by relating the size, shape and number of theapertures 38 to the volume and velocity of the air entering the cavity28. The pressure drop across the muffler 22 is primarily determined bythe annular area of the fixed orifices at}. In accordance with thismufiler construction, it is possible to preselect a desirablecombination of sound attenuation and motor back pressure; and, becausethe muffler comprises only rigid, fixed parts, these preselectedcharacteristics will not be subject to those objectionable variationscommonly encountered in conventional mufflers of the type describedhereinabove. Thus, an outstanding feature of this invention is that themotor speed of the illustrative tool is not affected by fluctuation inmufiler induced back pressure; and, the sound of the mutlled exhauststream is not subject to annoying changes in pitch and volume due tophysical changes in the structure of the muffler parts and resultingchanges in the exhaust flow pattern or speed of exhaust .fiow throughthe mufiler,

In the normal usage of hand-held air tools, it may be expected that themufiler will be subjected to random impacting and that the mother may bedisassembled and reassembled for periodic inspections. Such impactingand reassembly tend to cause the connection between threads 34 and 36 tobecome loose due to thread deformation and wear; therefore, it ispossible that the plug 24 will not threadably engage with the handle 16to properly clamp the sleeve 26 in the hereinbefore described manner. Asa result, the sleeve 26 may shift or wobble out of coaxial alignmentwith the plug 2.4 so that an optimum preset size and shape of theorifice 60 can no longer be maintained With the attending bad resultsthat the exhaust flow through the orifice may produce extraneous noiseand the pressure drop across the muffler may vary. These possible badresults do not occur in the mufiler 22, however, due to a self-centeringaction of the sleeve 26 about the longitudinal axis of the plug 2 Thusthe exhaust air will be emitted from the plug apertures 38 in anomnidirectional manner and will traverse the annular orifice 6d atsubstantially the same pressure and velocity at all points around thecircumference of t.e orifice 60. However, should the sleeve 26 driftlaterally causing the orifice 60 to lose its uniform cross sectionalshape, well understood dynamic and static pressure effects will operateon the skirt 50 to shift the skirt back into the desired coaxialrelation with the plug 24.

Another important feature of this invention is the provision of an airtool mufiler which is simply constructed and easy to assemble. In thisregard it will be appreciated that the muffler 22 comprises only twointerfitting parts, the plug 24 and the sleeve 26, which are unlikely tobe improperly assembled by inexperienced or careless workers. Moreover,when the mufiler is initially assembled or when it is reassembledfollowing inspection or repair, the tool may be energized briefly, justprior to finally tightening of the threads 32 and 34, so that the sleeve26 will center itself in the manner described above, and the sleeve canthereupon be finally clamped between the plug 26 and the handle 16 sothat the orifice at} is properly defined.

Another advantage of the mufiler 22 is that its assembled length and itsdiameter are such that the mufiler can be externally attached to thebottom surface 40 of the tool handle 16 without excessive protrusionbelow the handle and without extending beyond the side surfaces of thehandle. It will also be appreciated that by employing the plug 24 toclamp the sleeve 26 in place, the plug can be readily threaded intoproper relation with the handle 16 by a standard screwdriver which isengageable in the slot 45. This is an extremely advantageous method ofassembly for the mother 22 since, as shown in FIG. 3, the mufiler 22 anda fittng 62 for the air line 14 are necessarily closely spaced and itwould be difiicult to apply a wrench radially to the wall of the sleeve26.

It will be apparent to those skilled in the art that various changes inconstruction, proportion and arrangement of the described tool mufflermay be made without sacrificing any of the advantages of the inventionor departing from the scope of the pending claims.

Having fully described the invention, we claim:

ll. In combination:

(a) a pneumatic tool comprising:

(1) casing means including a handle portion;

(2) air motor means housed by said casing means;

(3) air supply passage means and exhaust passage means defined by saidcasing means and communicating with said motor means, said exhaustpassage means extending through said handle portion and opening to theexterior of said casing means; and

(b) exhaust muffler means attached to said casing means in communicationwith said exhaust passage means and comprising:

(1) a hollow member having a cavity for receiving exhaust from saidexhaust passage and havtherein communicating said cavity and saiddischarge means;

(4) said hollow member and said tubular member defining surface meansengageable to limit relative axial movement therebetween in onedirection;

(5) said tubular member having an annular end surface abutting with saidhandle portion about said opening of said exhaust passage means; and

(6) said tubular member being axially clamped at one end between saidhandle portion and said hollow member in coaxial relation with thelatter as the result of securing said hollow member to said handleportion.

2. The combination according to claim 1, wherein:

(a) said hollow member and said handle portion are provided withengageable threads; and

(b) said hollow member includes an end wall defining means cooperablewith an implement operable to produce engagement of said threads wherebysaid hollow member and said handle portion are secured together.

3. In combination:

(a) a pneumatic tool comprising:

( 1) casing means;

(2) air motor means housed by said casing means;

(3) air supply passage means and exhaust passage means defined by saidcasing means and communicating with said motor means; and

(b) exhaust muflier means attached to said casing means in communicationwith said exhaust passage means and comprising:

(1) a hollow member having a cavity for receiving exhaust from saidexhaust passage;

(2) a tubular member disposed about the exterior of said hollow memberand defining exhaust discharge means therebetween;

(3) said hollow member having aperture means therein communicating saidcavity and said discharge means;

(4) said exhaust discharge means including an annular orifice openingbetween the exterior of said hollow member and the interior of saidtubular member to atmosphere; and

(5 said tubular member being rigidly spaced from said hollow member toprovide said annular orifice with a uniform radial dimension about itsentire perimeter.

4. In combination: (a) a pneumatic tool comprising:

(1) casing means;

(2) air motor means housed by said casing means;

(3) air supply passage means and exhaust passage means defined by saidcasing means and communicating with said motor means; and

(b) exhaust mufller means attached to said casing means in communicationwith said exhaust passage means and comprising:

(1) a hollow member having a cavity for receiving exhaust from saidexhaust passage;

(2) a tubular member disposed about the exterior of said hollow memberand defining exhaust discharge means therebetween;

(3) said hollow member having aperture means therein communicating saidcavity and said discharge means; and

(4) said tubular member being rigidly clamped between said casing meansand said hollow member.

6 5. In combination: (a) a pneumatic tool comprising:

(1) casing means;

(2) air motor means housed by said casing means;

(3) air supply passage means and exhaust passage means defined by saidcasing means and communicating with said motor means; and

(b) exhaust muflier mean attached to said casing means in communicationwith said exhaust passage means and comprising:

(1) a hollow member having a cavity for receiving exhaust from saidexhaust passage;

(2) a tubular member disposed about the exterior of said hollow memberand defining exhaust discharge means therebetween; and

(3) said hollow member having aperture means therein communicating saidcavity and said discharge means;

(4) said tubular member including a flange portion and an integral skirtportion;

(5) said flange portion being rigidly clamped between said casing meansand said hollow member; and

(6) said skirt portion being held rigidly in coaxial alignment with saidhollow portion due to the clamping of said flange portion.

6. The combination according to claim 5, wherein:

said hollow member and said tubular member comprise one-piece, rigidmetal members.

7. In combination: (a) a pneumatic tool comprising:

(1) casing means including a handle portion;

(2) air motor means housed by said casing means;

(3) air supply passage means and exhaust passage means defined by saidcasing means and communicating with said motor means, said exhaustpassage means extending through said handle portion and opening to theexterior of said casing means; and

(b) exhaust mufiler means attached to said casing means in communicationwith said exhaust passage means and comprising:

(1) a hollow member having a cavity for receiving exhaust from saidexhaust passage and having a portion secured to said handle portion inthe opening of said exhaust passage;

(2) a tubular member disposed about the exterior of said hollow memberand defining exhaust discharge means therebetween;

(3) said hollow member having aperture means therein communicating saidcavity and said discharge means;

(4) said exhaust discharge means including an annular orifice openingbetween the exterior of said hollow member and the interior of saidtubular member to atmosphere; and

(5) said tubular member being uniformly spaced with respect to saidhollow member to provide said annular orifice with a uniform radialdimension about its entire perimeter.

References Cited UNITED STATES PATENTS 12/1900 Buck.

8/1960 Zwayer 18136 FOREIGN PATENTS ROBERT S. WARD, JR., PrimaryExaminer.

